Water based printable coatings

ABSTRACT

Various aqueous top coat compositions are described. The compositions include one or more polyurethane dispersions, silica, crosslinker(s), acrylic polymers, and an optional water soluble polyester. The compositions can be used to form top coats which exhibit good resistance to scratches and solvents, and improved ink retention.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/568,638 filed Dec. 12, 2014, now U.S. Pat. No. 9,777,191, whichclaims the benefit of U.S. Provisional Application No. 61/915,696 filedDec. 13, 2013, both of which are incorporated herein by reference intheir entireties.

BACKGROUND

The present subject matter relates to water based compositions. Thecompositions are well suited for coatings that can be applied to avariety of substrates for improving adhesion of inks and other printablecompositions. In particular, the present subject matter relates to topcoat compositions.

Coating compositions are known for applying to paper and polymeric filmsto provide or impart certain characteristics to the coated substrate.For example, top coats are known for providing a glossy surface or forproviding a particular appearance.

In many applications, films or other thin substrates are top coated toimprove adherence of printing media or inks. Improved adherence of printor deposited inks may also be indicated by increased resistance toabrasion, solvents, and/or environmental factors.

Although top coats having excellent performance with regard to one orseveral performance aspects are known, a need remains for top coatshaving a relatively wide range of performance characteristics.

SUMMARY

The difficulties and drawbacks associated with previously known coatingcompositions are addressed by the present subject matter top coatcompositions and coated substrates.

In one aspect, the present subject matter provides an aqueous top coatcomposition comprising 10 to 85 parts of one or more polyurethanes, 10to 60 parts of one or more water soluble polyesters, 0 to 80 parts ofacrylic polymer, and 0.01 to 3 parts of silica and 0.05 to 3 partscrosslinker.

In another aspect, the present subject matter provides a top coatedsubstrate comprising a polymeric substrate and an aqueous top coatcomposition disposed on the substrate. The top coat composition includes10 to 85 parts of one or more polyurethanes, 10 to 60 parts of one ormore water soluble polyesters, 0 to 80 parts of acrylic, and 0.01 to 3parts of silica, and 0.05 to 3 parts crosslinker.

As will be realized, the subject matter described herein is capable ofother and different embodiments and its several details are capable ofmodifications in various respects, all without departing from theclaimed subject matter. Accordingly, the description is to be regardedas illustrative and not restrictive.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present subject matter provides various compositions particularlyadapted for applying to substrates such as polymeric films to improveprinting characteristics and ink adherence properties. In particularembodiments, the compositions can be used as top coat compositions forpolymeric films such as polyester films, polypropylene films, andparticularly for bi-axially oriented polypropylene (BOPP) films. Thepresent subject matter compositions are also well suited for use as topcoat compositions for machine direction orientation (MDO) polymericfilms.

The compositions of the present subject matter generally comprise anaqueous blend or combination of (i) one or more polyurethane dispersionsto provide an effective amount of polyurethane solids, (ii) one or moreoptional water soluble polyesters, (iii) one or more optional acrylicpolymer, (iv) silica, and (v) one or more crosslinkers or crosslinkingagent(s). The compositions comprise components (i)-(v) mixed, blended,or otherwise incorporated in an aqueous vehicle.

Table 1 set forth below presents typical and particular weightproportions of components (i)-(v) in the present subject mattercompositions. The values in Table 1 are weight parts or dry parts byweight. In use, the components are combined with water in desiredamounts or incorporated in an aqueous vehicle to form a wide array ofcompositions such as for example top coat formulations.

TABLE 1 Top Coat Compositions Typical Range of Weight Particular Rangeof Components Proportions Weight Proportions Polyurethane 10-85 15-80Dispersion (solids) Water Soluble 10-60 15-25 Polyester (solids) Silica0.01-3   0.01-2   Acrylic (solids)  0-80 10-70 Crosslinker 0.05-3  0.10-1   Water — —

In particular embodiments, the polyurethane solids are provided via atleast two components, a dispersion of a “hard” polyurethane componentand a dispersion of a “soft” polyurethane component. An example of ahard polyurethane component suitable for use in a top coat compositionof the present subject matter is BAYHYDROL® UH XP 2719 available fromBayer Material Science. BAYHYDROL® UH XP 2719 is an aliphatic,polyester-based anionic polyurethane dispersion. An example of a softpolyurethane component suitable for use in a top coat composition of thepresent subject matter is NEOREZ™ R-9621 available from DSM NeoResins.NEOREZ™ R-9621 is an aliphatic polyester waterborne urethane. Anothernon-limiting example of a suitable water based polyurethane isBondthane™ UD-104 produced by Bond Polymers International. Yet anothernon-limiting example of a suitable water based polyurethane dispersionis Unithane SX-487SF supplied Union Specialties. In the compositions ofthe present subject matter, Unithane may be used either alone or blendedwith other polyurethanes.

The compositions of the present subject matter optionally comprise oneor more water soluble polyesters. In many embodiments, this component isin the form of a water dispersible, linear polyester prepared from thepolycondensation of glycols and dicarboxylic acids, at least some ofwhich contain functional groups such as but not limited to, sulfonatesalts (—SO₃M), carboxyl groups (—COOH), and combinations thereof.Typical molecular weights for the polyester range from about 5,000 toabout 20,000 with 10,000 to 14,000 being useful for many applications.Typical glass transition (Tg) temperatures range from about 36° C. toabout 52° C. with 42° C. to 46° C. being useful for certain embodiments.A nonlimiting example of a suitable water polyester is SKYBON EW 100Qavailable from SK Chemicals.

The present subject matter compositions also comprise one or more silicacomponent(s). Typically, the silica component is in the form ofamorphous silica having an average particular size of from about 4 μm toabout 6 μm, and for particular embodiments from 4.3 μm to 5.3 μm. Anonlimiting example of a suitable silica component is SYLOBLOC® 45available from Grace Davison Engineered Materials.

The present subject matter compositions also comprise one or morecrosslinkers or crosslinking agents that serve to crosslink or at leastpromote crosslinking of the polyurethane component(s). A particularlyuseful crosslinker is an aziridine, or carbodiimide crosslinker. Anonlimiting example of an aziridine crosslinker is CX-100 available fromDSM NeoResins. CX-100 is a polyfunctional aziridine liquid crosslinker.

The present subject matter compositions can include additionalcomponents. For example, when formulating a top coat composition to beused with an acrylate-containing ink, it may be beneficial to includeone or more acrylic polymers in the top coat composition. Typicalconcentrations of the acrylic polymers in the top coat composition mayrange from about 0% to about 85%. A nonlimiting example of a suitableacrylic polymer is a 100% acrylic emulsion polymer available under thedesignation NeoCryl® FL-791 XP from DSM NeoResins. The present subjectmatter compositions may also comprise one or more antiblock agents. Whenforming top coats on polymeric films with polymeric release liners,incorporation of antiblock agents may be beneficial. The present subjectmatter compositions may also comprise one or more defoamers. Anonlimiting example of a suitable defoamer is Dehydran® 1620 defoamerproduced by BASF.

Additional processing can be performed upon either the surface toreceive the top coat formulation, or upon the top coat layer, or both.For example, corona treatment may be performed upon the surface toreceive the top coat, prior to applying the top coat. Alternatively orin addition, corona treatment may be performed upon a previously appliedand formed top coat.

Useful top coat compositions can be prepared by addition of water to thenoted components. It will be understood that certain components mayinclude water such as for example the polyurethane dispersion(s) and thepolyester. Thus, the water associated with those components may besufficient to achieve a desired water content for the resultingcomposition. Alternatively, additional amounts of water are added toproduce an aqueous top coat composition with properties and/orcharacteristics as desired.

Table 2 lists representative and particular top coat compositions A andB in accordance with the present subject matter. The percentages inTable 2 are weight percentages based upon the total weight (includingwater) of the resulting top coat composition.

TABLE 2 Top Coat Compositions A and B Top Coat A Quantity Top Coat BQuantity Ingredient (%) (%) Bayhydrol UH XP 2719 22.50 37.50 Sylobloc 450.33 0.33 CX-100 0.50 0.15 Water 0.90 35.70 Neorez R-9621 15.77 26.32 EW100Q Solution (25%) 60.00 — Total 100.00 100.00

The compositions such as top coat compositions can be applied to asurface or substrate using a wide array of techniques and methods. Whenapplying as a top coat to a polymeric film, conventional applicationtechniques can be used. Representative coat weights for top coats inaccordance with the present subject matter range from about 0.1 to about1.0 grams per square meter (gsm), and in particular embodiments from 0.5gsm to 0.6 gsm.

Typically, after application to a surface of interest such as apolymeric film, the resulting coating is dried and allowed tosufficiently cure, i.e., crosslink. As will be appreciated, the timeperiod for drying depends upon several factors including the dryingtemperature and the amount of water and/or other vehicles or solventpresent in the coated composition. The present subject matter includesdrying at ambient temperatures or drying at elevated temperatures suchas by heating. An advantage of using an aziridine crosslinking agent isthat typically crosslinking can occur at ambient temperatures and thusheat is not necessary to effect curing. Typically, top coats aresuitably dried and/or cured after a time period of about 12 hours ormore, in certain embodiments after a time period of 24 hours or more, inother embodiments after a time period of 48 hours or more, in stillother embodiments after a time period of 72 hours or more.

After application, drying, and crosslinking of the top coats inaccordance with the present subject matter, a durable, print-receptivesurface is formed. The resulting top coats can receive print, inks, orother similar compositions and promote bonding and/or adherence of theprint, ink, or like composition to the underlying top coat.

The top coat compositions of the present subject matter are particularlyadapted for receiving print or other indicia which is applied by thermaltransfer means, such as for example by thermal transfer ribbons carryingwaxy resins as known in the art. The top coat compositions are also wellsuited for receiving UV curable flexo inks or water based flexo inks asknown in the art. In certain embodiments and/or applications, top coatsof the present subject matter can be used in conjunction with all ofthese printing techniques and/or inks.

The top coat compositions of the present subject matter exhibit goodresistance to scratches, nicking, and scuffing. The top coatcompositions of the present subject matter also exhibit good resistanceto solvents and environmental factors.

Additional aspects and details of top coat compositions, componentsthereof, and processing and application thereof are described in WO02/062894, herein incorporated by reference. For example, in certainembodiments top coats of the present subject matter may include one ormore of the components described in the WO '894 publication.

EXAMPLES

A series of investigations were undertaken to evaluate (i) scratchresistance, (ii) ink adhesion, and (iii) solvent resistance of a topcoat composition in accordance with the present subject matter ascompared to several other top coats.

Specifically, four (4) top coat formulations were obtained or prepared.Top coat C was a top coat formulation from Supplier A. Top coat D was atop coat formulation from Supplier B. Top coat E was a top coatformulation in accordance with the present subject matter. And, top coatF was a top coat formulation available from Avery Dennison.

Each top coat formulation was applied to a substrate. Printing bythermal transfer, or printing using UV curable flexo ink or water-basedflexo ink (at either 100 feet per minute (fpm) or 300 fpm) was performedupon the top coats, as described herein. Several top coated samples alsoreceived corona treatment.

After preparation, i.e., coating, drying, and curing, of the top coatedsamples, and deposition of print thereon, the samples were subjected toscratch resistance testing, ink adhesion evaluation, and solventresistance testing.

Particular types of scratch resistance and ink adhesion evaluations wereperformed depending upon whether print was applied by thermal transferor using flexo inks.

For samples that received printing by thermal transfer ribbons (ribbonsDNP R-510HF and ITW B324), each printed sample was subjected to fifty(50) rubs applied using a Crocker meter as known in the art. The sampleswere then read by a Trucheck Verifier as known in the art to obtain anANSI (American National Standard Institute) number. That number providesan indication as to the extent of ink that was removed as a result ofthe Crocker meter. A higher number corresponds to a higher resistance toscratching.

For samples that received printing by application of UV curable flexoink or water-based flexo ink, a “cross hatch” test and a “nickelscratch” test were used. The cross hatch test involves subjecting theprinted ink face of the samples to a series of scratches applied in across hatch fashion, and then applying an adhesive tape onto thescratched face. The tape is then removed and if sufficiently scratched,regions of printed ink dislodged from the top coat become adhered to thetape and are removed from the sample upon tape removal. The tape used is810 Tape available from 3M. A subjective rating was then assigned to thesample after tape removal in which a high score designated a high degreeof print or ink adhesion, i.e., low amount of ink retained on the tapeafter removal.

The nickel scratch test involves subjecting the printed ink face of thesamples to scratching from a nickel coin rubbed across the printed faceof the sample. The scratching resulting from the nickel scratch test isharsher than that resulting from the cross hatch test. A subjectiverating was then assigned to the sample after scratching. A high scoredesignated a high degree of print or ink adhesion, i.e., low degree ofscratching resulting from the nickel.

Table 3A summarizes the results of scratch resistance and ink adhesionfor samples printed by thermal transfer ribbons.

TABLE 3A Performance of Top Coats with Thermal Transfer Printing TopCoat Printing C D E F Thermal Transfer 10 3 9 2

The values in Table 3A are the average results from the Crocker meteranalysis. Higher values are better. Top coat E in accordance with thepresent subject matter exhibited excellent performance.

Table 3B summarizes the results of scratch resistance and ink adhesionfor samples printed using UV curable flexo inks. Table 3B presentsvalues which are the sum of the scores of the previously described crosshatch test and nickel scratch test. Table 3B presents the sum of scoresfor samples that were not corona treated. The printing experiment wasdone at 100 fpm and 300 fpm at 2 Billion Cubic Microns (BCM).

TABLE 3B Performance of Top Coats and Flexo Inks, Without CoronaTreatment Top Coat Printing C D E F UV Flexo 15 14 14 6 Substrate BOPPBOPP BOPP BOPP

As evident from the testing results summarized in Table 3B, the overallperformance of a top coat in accordance with the present subject matter,i.e., Top coat E, exhibited the same relatively good performance for UVflexo inks as compared to the top coats from Supplier A and Supplier B,i.e., Top coats C and D.

Solvent resistance was evaluated by preparing samples of the presentsubject matter top coated on white PET film. Similar samples using topcoat formulations from Supplier A and Supplier B were prepared. The topcoated samples received print by thermal transfer using a DNP R-510HFribbon, and also by an ITW B324 ribbon.

Solvent resistance was assessed by using a numerical rating system inwhich a low score indicates a relatively high degree of removal ordissolving of top coat material after exposure to solvent(s); and a highscore indicates good resistance to the solvent(s). For solventresistance evaluation, top coated samples were thermal transfer printed,aged for 24 hours, and then soaked in a solvent bath for 1 hour. Thesolvent bath was a 50/50 mixture of toluene and kerosene. After removalfrom the bath, the printed or ink coated samples were then thumb rubbedan equal number of times. This solvent resistance evaluation isgenerally in accordance with the procedure described in standard UL 969.

Comparison of the various samples after soaking in solvent followed byfinger rubbing indicated that the samples that were top coated inaccordance with the present subject matter exhibited comparableperformance as samples having other commercially available top coats.

To further improve the UV flexo printing performance, Top coat E wasmodified to G, H, and J. The formulations were prepared and top coatedon polyester film using the Meyer rod technique.

TABLE 4 Top Coat Compositions E, G, H, and J Top Coat Top Coat Top CoatTop Coat E Qty G Qty H Qty J Qty Ingredient (%) (%) (%) (%) Bayhydrol UHXP 2719 29.5 31.4 6.3 0 Unithane SX-487SF 0 0 0 14.34 Sylobloc 45 0.430.5 0.5 0.46 Dehydran 1620 0.01 0 0 0 CX-100 0.65 0.3 0.3 0.3 Water29.01 10.9 16.2 14.71 Neorez R-9621 20.66 22 0 0 Bondthane UD-104 0 06.6 0 EW 100Q solution (25%) 19.64 0 0 0 EW 100Q solution (15%) 0 34.834.8 34.85 Ammonia 19% 0.1 0.1 0 0 Neocryl FL-791 XP 0 0 35.3 35.34Total 100 100 100 100The results are summarized in Table 4A below. The printing was performedusing a lab unit (Flexi UV printer) printing at 150 fpm at 3 BCM.

TABLE 4A Performance of Top Coats and UV Flexo Inks, Without CoronaTreatment Top Coat Printing C E G H J UV Flexo 10 8 10 10 10The results are based on “Cross Hatch Adhesion Test” using A10tape-higher values are better. The performance of G, H, and Jformulations was equivalent to that of formulation C. Top coat G and Halso have good solvent resistance based on UL 969 test when DNP R-510HFribbon is used in thermal transfer printing. Additionally, Top coat Hhas good laser printing quality.

Many other benefits will no doubt become apparent from futureapplication and development of this technology.

All patents, published applications, standards, and articles notedherein are hereby incorporated by reference in their entirety.

As described hereinabove, the present subject matter solves manyproblems associated with previous strategies, systems and/or devices.However, it will be appreciated that various changes in the details,materials and arrangements of components, which have been hereindescribed and illustrated in order to explain the nature of the presentsubject matter, may be made by those skilled in the art withoutdeparting from the principle and scope of the claimed subject matter, asexpressed in the appended claims.

What is claimed is:
 1. An aqueous top coat composition comprising: 10 to85 parts by weight of one or more polyurethanes; 10 to 60 parts byweight of one or more water soluble polyesters; 0 to 80 parts by weightof one or more acrylic polymers; 0.01 to 3 parts by weight of silica;0.05 to 3 parts by weight crosslinker; wherein the aqueous top coatcomposition comprises from 20 to 99.04% solids.
 2. The top coatcomposition of claim 1, wherein the polyurethanes include a hardpolyurethane and a soft polyurethane.
 3. The top coat composition ofclaim 1, wherein the water soluble polyester is a linear polyesterprepared from the polycondensation of glycols and dicarboxylic acids andhas a molecular weight from 5,000 to 20,000.
 4. The top coat compositionof claim 3, wherein the polyester has a glass transition temperature Tgfrom 36° C. to 52° C.
 5. The top coat composition of claim 1, whereinthe crosslinker includes an aziridine crosslinker.
 6. The top coatcomposition of claim 1, wherein the composition comprises from 10 to 70parts by weight of one or more acrylic polymers.
 7. The top coatcomposition of claim 1, further comprising at least one additionalcomponent selected from the group consisting of an antiblock agent, anacrylic polymer, and combinations thereof.
 8. The top coat compositionof claim 1, further comprising water in addition to water found with anyof the other components of the top coat composition.
 9. A top coatedsubstrate comprising: a polymeric substrate; a top coat disposed on thesubstrate, the top coat including 10 to 85 parts by weight of one ormore polyurethanes, 0 to 80 parts by weight of one or more acrylicpolymers, 10 to 60 parts by weight of one or more water solublepolyesters, 0.01 to 3 parts by weight of silica, and 0.05 to 3 parts byweight crosslinkers; wherein the top coat is print receptive.
 10. Thetop coated substrate of claim 9, wherein the substrate is bi-axiallyoriented polypropylene (BOPP).
 11. The top coated substrate of claim 9,wherein the substrate is machine direction orientation (MDO) film. 12.The top coated substrate of claim 9, wherein the substrate is polyesterfilm.
 13. The top coated substrate of claim 9, wherein the polyurethanesinclude a hard polyurethane and a soft polyurethane.
 14. The top coatedsubstrate of claim 9, wherein the water soluble polyester is a linearpolyester prepared from the polycondensation of glycols and dicarboxylicacids and has a molecular weight from 5,000 to 20,000.
 15. The topcoated substrate of claim 9, wherein the polyester has a glasstransition temperature Tg from 36° C. to 52° C.
 16. The top coatedsubstrate of claim 9, wherein the crosslinker includes an aziridinecrosslinker.
 17. The top coated substrate of claim 9, wherein thecomposition comprises from 12 to 27 parts by weight of polyurethanes.18. The top coated substrate of claim 9, wherein the compositioncomprises from 15 to 25 parts by weight of water soluble polyesters. 19.The top coated substrate of claim 9, wherein the composition comprisesfrom 0.01 to 2 parts by weight silica.
 20. The top coated substrate ofclaim 9, wherein the composition comprises from 0.05 to 1 parts byweight crosslinker.